This Pyrex® manometer tube is enclosed in a round bottom, graduated jacket and is sealed to a stopcock plug. In use, mercury is placed in the inner tube and in the jacket bottom to measure the pressure differential. Not recommended for positive pressure. The legible, red scale ranges from 0 to 160mm. Mercury filling instructions are supplied with each instrument. Uses 5 to 6mL mercury which is not supplied. Scale: 0 = 760mm (Full Vac.) 80 = 680mm, 160 = 600mm.